[media] v4l2: add core support for the new VIDIOC_ENUM_FREQ_BANDS ioctl

This adds the usual core support code for this new ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>